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<head><meta charset="utf-8"><title>process for finding/filing underlying LLVM bugs rust#74498 · t-compiler/wg-llvm · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/index.html">t-compiler/wg-llvm</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html">process for finding/filing underlying LLVM bugs rust#74498</a></h3>

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<a name="205655809"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205655809" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205655809">(Aug 01 2020 at 00:47)</a>:</h4>
<p>Hi all, I was going through <a href="https://github.com/rust-lang/rust/issues/74498">rust#74498</a> and have independently confirmed the analysis there that indicates that this is an LLVM <code>-loop-optimize</code> bug</p>



<a name="205655859"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205655859" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205655859">(Aug 01 2020 at 00:48)</a>:</h4>
<p>but I couldn't tell if any of the participants on the rust issue (<a href="https://github.com/rust-lang/rust/issues/74498">rust#74498</a>) had actually filed such a bug, or tracked one down?</p>



<a name="205655889"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205655889" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205655889">(Aug 01 2020 at 00:49)</a>:</h4>
<p>I did a couple naive searches on <a href="https://bugs.llvm.org/">https://bugs.llvm.org/</a>, but couldn't find anything obvious (namely, new bugs that either mention <a href="https://github.com/rust-lang/rust/issues/74498">#74498</a>, or that mention <code>add nuw</code> under the <code>Loop Optimizer</code> component...)</p>



<a name="205655953"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205655953" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205655953">(Aug 01 2020 at 00:50)</a>:</h4>
<p>cc <span class="user-mention" data-user-id="198590">@comex</span> <span class="user-mention" data-user-id="133224">@Nikita Popov</span> <span class="user-mention" data-user-id="132778">@Luqman Aden</span></p>



<a name="205655978"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205655978" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205655978">(Aug 01 2020 at 00:50)</a>:</h4>
<p>basically, I am asking 1. if any of you can point me at an already filed bug for this, and more generally 2. what process would <em>you use</em> to find such a bug, or find an already filed record of the same bug?</p>



<a name="205656044"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656044" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656044">(Aug 01 2020 at 00:52)</a>:</h4>
<p>(while I await responses here, I will start drafting a bug to file on <a href="http://bugs.llvm.org">bugs.llvm.org</a>. But I figure an already filed bug is likely to have more useful stuff in it than what I would file. Or at least, it would represent less labor <em>for me</em>. <span aria-label="wink" class="emoji emoji-1f609" role="img" title="wink">:wink:</span> )</p>



<a name="205656702"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656702" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656702">(Aug 01 2020 at 01:09)</a>:</h4>
<p>people will very rarely file bugs against llvm itself with llvm-ir reproducers.</p>



<a name="205656748"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656748" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656748">(Aug 01 2020 at 01:10)</a>:</h4>
<p>because they'd prefer C source to feed to clang?</p>



<a name="205656749"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656749" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656749">(Aug 01 2020 at 01:10)</a>:</h4>
<p>more commonly you're going to find stuff like "<code>clang</code> doesn't terminate"</p>



<a name="205656776"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656776" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656776">(Aug 01 2020 at 01:11)</a>:</h4>
<p>I'd say its because that's how people are most likely to hit said bugs. And reporting bugs against clang is an easy way to not do must investigation.</p>



<a name="205656777"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656777" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656777">(Aug 01 2020 at 01:11)</a>:</h4>
<p>well, okay: I can believe that it may be foolish to expect to find a useful bug already filed</p>



<a name="205656795"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656795" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656795">(Aug 01 2020 at 01:11)</a>:</h4>
<p>but I am also curious about what the LLVM dev's themselves would <em>prefer</em></p>



<a name="205656849"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656849" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656849">(Aug 01 2020 at 01:12)</a>:</h4>
<p>i.e. if I take the .ll file that demonstrates the issue, and package it up nicely with some C code that you can link it to in order to observe the problem directly ...</p>



<a name="205656852"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656852" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656852">(Aug 01 2020 at 01:12)</a>:</h4>
<p>... are they more likely to be able to work with such a bug report?</p>



<a name="205656865"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656865" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656865">(Aug 01 2020 at 01:13)</a>:</h4>
<p>I guess this does diverge from my original question, which was about searching for already filed bugs, rather than hypothesizing what kind of bugs the LLVM devs <em>want</em> to see...</p>



<a name="205656868"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656868" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656868">(Aug 01 2020 at 01:13)</a>:</h4>
<p>Its fine to report with llvm-ir</p>



<a name="205656878"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656878" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656878">(Aug 01 2020 at 01:13)</a>:</h4>
<p>here's another way of looking at my question</p>



<a name="205656880"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656880" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656880">(Aug 01 2020 at 01:13)</a>:</h4>
<p>reading the comment thread on <a href="https://github.com/rust-lang/rust/issues/74498">#74498</a> ...</p>



<a name="205656887"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656887" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656887">(Aug 01 2020 at 01:14)</a>:</h4>
<p>... I see references to <em>already known</em> bugs</p>



<a name="205656923"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656923" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656923">(Aug 01 2020 at 01:14)</a>:</h4>
<p>Presuming there was due diligence done to actually minimize the IR itself.</p>



<a name="205656934"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656934" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656934">(Aug 01 2020 at 01:14)</a>:</h4>
<p>using acronyms like LFTR and LSR</p>



<a name="205656942"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656942" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656942">(Aug 01 2020 at 01:14)</a>:</h4>
<p>(The IR is pretty mnimal, see <a href="https://github.com/rust-lang/rust/issues/74498#issuecomment-661950983">https://github.com/rust-lang/rust/issues/74498#issuecomment-661950983</a> )</p>



<a name="205656955"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656955" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656955">(Aug 01 2020 at 01:15)</a>:</h4>
<p>(its hard to imagine something more minimal ; the problem I have with an example like that is that I am not good at reading such text and being able to tell if it is already hitting UB)</p>



<a name="205656959"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205656959" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205656959">(Aug 01 2020 at 01:15)</a>:</h4>
<p>(but that's mostly because I am out-of-practice w.r.t. reading LLVM IR)</p>



<a name="205657004"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657004" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657004">(Aug 01 2020 at 01:16)</a>:</h4>
<p><span class="user-mention silent" data-user-id="116083">pnkfelix</span> <a href="#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498/near/205656887">said</a>:</p>
<blockquote>
<p>... I see references to <em>already known</em> bugs</p>
</blockquote>
<p><span class="user-mention silent" data-user-id="116083">pnkfelix</span> <a href="#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498/near/205656934">said</a>:</p>
<blockquote>
<p>using acronyms like LFTR and LSR</p>
</blockquote>
<p>but I don't know how to find the referenced bugs; no URLs were provided</p>



<a name="205657012"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657012" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657012">(Aug 01 2020 at 01:17)</a>:</h4>
<p>and I assume that if I had a way to find those bugs, I might be able to quickly see if there's already a bug filed about this.</p>



<a name="205657016"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657016" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657016">(Aug 01 2020 at 01:17)</a>:</h4>
<p><span class="user-mention silent" data-user-id="116083">pnkfelix</span> <a href="#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498/near/205657004">said</a>:</p>
<blockquote>
<p><span class="user-mention silent" data-user-id="116083">pnkfelix</span> <a href="#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498/near/205656887">said</a>:</p>
<blockquote>
<p>... I see references to <em>already known</em> bugs</p>
</blockquote>
<p><span class="user-mention silent" data-user-id="116083">pnkfelix</span> <a href="#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498/near/205656934">said</a>:</p>
<blockquote>
<p>using acronyms like LFTR and LSR</p>
</blockquote>
<p>but I don't know how to find the referenced bugs; no URLs were provided</p>
</blockquote>
<p>Might be because <span class="user-mention" data-user-id="133224">@Nikita Popov</span> actually fixed said bug(s): <a href="https://reviews.llvm.org/D60935">https://reviews.llvm.org/D60935</a></p>



<a name="205657024"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657024" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657024">(Aug 01 2020 at 01:17)</a>:</h4>
<p>okay that helps</p>



<a name="205657027"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657027" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657027">(Aug 01 2020 at 01:17)</a>:</h4>
<p>since I might be able to go from that to the issue it fixed</p>



<a name="205657028"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657028" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657028">(Aug 01 2020 at 01:17)</a>:</h4>
<p>and see if people noted this other instance</p>



<a name="205657081"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657081" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657081">(Aug 01 2020 at 01:18)</a>:</h4>
<p>(or a bunch of similar hits for lftr-related fixes on phab)</p>



<a name="205657089"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657089" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657089">(Aug 01 2020 at 01:19)</a>:</h4>
<p>if nothing else, reading <a href="https://bugs.llvm.org/show_bug.cgi?id=31181">https://bugs.llvm.org/show_bug.cgi?id=31181</a> shows me how other people structure similar bugs</p>



<a name="205657153"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657153" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657153">(Aug 01 2020 at 01:20)</a>:</h4>
<p>and i see, I was probably wrong to assume that such bugs would be filed against the Loop Optimizer component; 31181 was filed against Scalar Optimizations, at least...</p>



<a name="205657172"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657172" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657172">(Aug 01 2020 at 01:21)</a>:</h4>
<p>Yeah, I wouldn’t say that categorization in LLVM bugzilla is maintained very well.</p>



<a name="205657176"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657176" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657176">(Aug 01 2020 at 01:21)</a>:</h4>
<p>although the reproducer in our case is literally using just <code>opt -loop-reduce</code> ...</p>



<a name="205657233"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657233" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657233">(Aug 01 2020 at 01:22)</a>:</h4>
<p>It isn't always easy to root cause the problem at the time of filling and their categories very much want that.</p>



<a name="205657355"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657355" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657355">(Aug 01 2020 at 01:26)</a>:</h4>
<p>can you explain to me what the <code>nuw</code>  in <code>add nuw</code> is supposed to mean when you are adding signed values?</p>



<a name="205657362"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657362" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657362">(Aug 01 2020 at 01:26)</a>:</h4>
<p>(I'm still sitting here trying to understand whether this is UB)</p>



<a name="205657386"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657386" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657386">(Aug 01 2020 at 01:27)</a>:</h4>
<p>I guess an unsigned overflow is going from -1 to 0, but it is <em>not</em> going from MAX to MIN?</p>



<a name="205657390"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657390" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657390">(Aug 01 2020 at 01:27)</a>:</h4>
<p>(for signed values, that is)</p>



<a name="205657392"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657392" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657392">(Aug 01 2020 at 01:27)</a>:</h4>
<p>is that right?</p>



<a name="205657436"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657436" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657436">(Aug 01 2020 at 01:28)</a>:</h4>
<p>or wait, what I just said doesn't make sense, does it</p>



<a name="205657462"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657462" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657462">(Aug 01 2020 at 01:29)</a>:</h4>
<p>no-unsigned-wrap</p>



<a name="205657523"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657523" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657523">(Aug 01 2020 at 01:30)</a>:</h4>
<p>but the inputs are <em>signed</em>. Isn't an unsigned wrap when you do <code>1 + (unsigned)-1</code> ?</p>



<a name="205657524"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657524" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657524">(Aug 01 2020 at 01:30)</a>:</h4>
<p>so basically operation result doesn’t go below 0 or above MAX.</p>



<a name="205657537"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657537" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657537">(Aug 01 2020 at 01:31)</a>:</h4>
<p>I'm probably making this more confusing</p>



<a name="205657548"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657548" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657548">(Aug 01 2020 at 01:31)</a>:</h4>
<p><span class="user-mention" data-user-id="116083">@pnkfelix</span> what do you mean signed? Is that conceptual (i.e. language source level) property? At LLVM IR there’s no distinction between signed and unsigned in types anymore</p>



<a name="205657552"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657552" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657552">(Aug 01 2020 at 01:31)</a>:</h4>
<p>is the <code>nuw</code> flag indicating that you will never attempt to overflow the maximal unsigned value?</p>



<a name="205657593"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657593" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657593">(Aug 01 2020 at 01:32)</a>:</h4>
<p>i32 is just 32 bits of space and the signedness of an operation is decided at instruction level.</p>



<a name="205657598"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657598" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657598">(Aug 01 2020 at 01:32)</a>:</h4>
<p><span class="user-mention silent" data-user-id="116083">pnkfelix</span> <a href="#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498/near/205657552">said</a>:</p>
<blockquote>
<p>is the <code>nuw</code> flag indicating that you will never attempt to overflow the maximal unsigned value?</p>
</blockquote>
<p>yes.</p>



<a name="205657607"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657607" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657607">(Aug 01 2020 at 01:32)</a>:</h4>
<p>For addition that's what it would mean, since signed addition and unsigned addition are one and the same thing.</p>



<a name="205657619"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657619" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657619">(Aug 01 2020 at 01:33)</a>:</h4>
<p>and the maximal unsigned value, under two's complement, is <code>(unsigned)-1</code>, right?</p>



<a name="205657625"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657625" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657625">(Aug 01 2020 at 01:33)</a>:</h4>
<p>Right.</p>



<a name="205657679"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657679" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657679">(Aug 01 2020 at 01:34)</a>:</h4>
<p>so that is what is confusing me about this code:</p>
<div class="codehilite"><pre><span></span><code>  %3 = icmp eq i8 %2, -1
  %4 = add nuw i8 %2, 1
  br i1 %3, label %5, label %1
</code></pre></div>



<a name="205657688"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657688" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657688">(Aug 01 2020 at 01:34)</a>:</h4>
<p>that's in a loop</p>



<a name="205657704"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657704" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657704">(Aug 01 2020 at 01:35)</a>:</h4>
<p>where the phi node has <code>%2</code> gets <code>%4</code>'s value</p>



<a name="205657709"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657709" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657709">(Aug 01 2020 at 01:35)</a>:</h4>
<p>u-huh.</p>



<a name="205657726"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657726" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657726">(Aug 01 2020 at 01:36)</a>:</h4>
<p>so the <code>%2</code> is <em>going</em> to hit <code>-1</code>, and then we'll do the add before we do the <code>br</code></p>



<a name="205657752"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657752" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657752">(Aug 01 2020 at 01:36)</a>:</h4>
<p>right?</p>



<a name="205657756"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657756" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657756">(Aug 01 2020 at 01:36)</a>:</h4>
<p>hm.</p>



<a name="205657758"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657758" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657758">(Aug 01 2020 at 01:36)</a>:</h4>
<p>Isn't that UB?</p>



<a name="205657761"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657761" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657761">(Aug 01 2020 at 01:36)</a>:</h4>
<blockquote>
<p>If the nuw and/or nsw keywords are present, the result value of the add is a poison value if unsigned and/or signed overflow, respectively, occurs.</p>
</blockquote>
<p>As per <a href="https://llvm.org/docs/LangRef.html#id86">https://llvm.org/docs/LangRef.html#id86</a></p>



<a name="205657767"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657767" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657767">(Aug 01 2020 at 01:37)</a>:</h4>
<p>ah</p>



<a name="205657769"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657769" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657769">(Aug 01 2020 at 01:37)</a>:</h4>
<p>poison flows into <code>%4</code></p>



<a name="205657771"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657771" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657771">(Aug 01 2020 at 01:37)</a>:</h4>
<p>but then we break out</p>



<a name="205657774"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657774" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657774">(Aug 01 2020 at 01:37)</a>:</h4>
<p>so the poison doesn't matter</p>



<a name="205657775"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657775" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657775">(Aug 01 2020 at 01:37)</a>:</h4>
<p>is that right?</p>



<a name="205657823"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657823" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657823">(Aug 01 2020 at 01:38)</a>:</h4>
<p>Yeah, we break out with <code>br i1 %3, label %5, label %1</code> before the poison value in <code>%4</code> is ever used.</p>



<a name="205657836"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657836" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657836">(Aug 01 2020 at 01:38)</a>:</h4>
<p>Okay. I guess I've managed to convince myself that comex's example should work and that I shouldn't be embarrassed to post it in a bug report.</p>



<a name="205657839"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657839" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657839">(Aug 01 2020 at 01:38)</a>:</h4>
<p>(or rather, you've convinced me)</p>



<a name="205657858"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657858" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657858">(Aug 01 2020 at 01:40)</a>:</h4>
<p>There’s a bunch of stuff on poison values on that same page as well: <a href="https://llvm.org/docs/LangRef.html#poisonvalues">https://llvm.org/docs/LangRef.html#poisonvalues</a></p>



<a name="205657921"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205657921" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205657921">(Aug 01 2020 at 01:41)</a>:</h4>
<p>If I’m reading that one correctly it isn’t even a problem for poison to be selected by a <code>phi</code>.</p>



<a name="205658135"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205658135" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205658135">(Aug 01 2020 at 01:46)</a>:</h4>
<p>wow I really am disliking bugzilla workflow</p>



<a name="205658140"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205658140" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205658140">(Aug 01 2020 at 01:47)</a>:</h4>
<p>and I used it, for like, years...</p>



<a name="205658836"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205658836" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205658836">(Aug 01 2020 at 02:05)</a>:</h4>
<p>Filed <a href="https://bugs.llvm.org/show_bug.cgi?id=46943">https://bugs.llvm.org/show_bug.cgi?id=46943</a> with LLVM upstream</p>



<a name="205658885"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205658885" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205658885">(Aug 01 2020 at 02:06)</a>:</h4>
<p>does LLVM have an easy way to get at previous released binaries, analgous to what we use for <code>cargo-bisect-rustc</code>?</p>



<a name="205659024"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205659024" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205659024">(Aug 01 2020 at 02:11)</a>:</h4>
<p>IIRC LLVM doesn't guarantee master is buildable even, so probably no?</p>



<a name="205659485"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205659485" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205659485">(Aug 01 2020 at 02:25)</a>:</h4>
<p>oh yeah</p>



<a name="205659489"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205659489" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205659489">(Aug 01 2020 at 02:25)</a>:</h4>
<p>I guess the time we spend doing those bors runs <strong>does</strong> have <em>some</em> benefits, doesn't it? <span aria-label="laughing" class="emoji emoji-1f606" role="img" title="laughing">:laughing:</span></p>



<a name="205659549"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205659549" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205659549">(Aug 01 2020 at 02:26)</a>:</h4>
<p>I'm attempting to check locally if bisection would make any sense here, just by going back a couple LLVM releases and seeing if the bug was there too</p>



<a name="205659562"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205659562" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205659562">(Aug 01 2020 at 02:27)</a>:</h4>
<p>unfortunately the LLVM IR syntax was more restrictive back in LLVM 8 ...</p>



<a name="205660361"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205660361" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205660361">(Aug 01 2020 at 02:51)</a>:</h4>
<p>(so far, I've seen it in LLVM 9, 8, 7, and 6 ...)</p>



<a name="205660415"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205660415" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205660415">(Aug 01 2020 at 02:52)</a>:</h4>
<p>and I'm guessing that when I <em>do</em> hit a release that doesn't have the incorrect LSR optimization, it will be because its LSR was just less aggressive</p>



<a name="205660422"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205660422" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205660422">(Aug 01 2020 at 02:52)</a>:</h4>
<p>(i.e. it won't be a narrow injection that's easy to fix)</p>



<a name="205661166"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205661166" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205661166">(Aug 01 2020 at 03:16)</a>:</h4>
<p>Heh. I may have just found the bug. Or at least, there's something that seems like it might tie quite strongly into the conversation that <span class="user-mention" data-user-id="123586">@nagisa</span> and I were having up above</p>



<a name="205661223"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205661223" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205661223">(Aug 01 2020 at 03:18)</a>:</h4>
<p>namely, check out this line: <a href="https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp#L2112">https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp#L2112</a></p>



<a name="205661228"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205661228" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205661228">(Aug 01 2020 at 03:18)</a>:</h4>
<p><code>if (!IsSigned &amp;&amp; !AR-&gt;hasNoUnsignedWrap()) continue;</code></p>



<a name="205661251"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205661251" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205661251">(Aug 01 2020 at 03:19)</a>:</h4>
<p>that is, I bet that should just be <code>if (!AR-&gt;hasNoUnsignedWrap()) continue;</code></p>



<a name="205662138"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/process%20for%20finding/filing%20underlying%20LLVM%20bugs%20rust%2374498/near/205662138" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> pnkfelix <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/process.20for.20finding.2Ffiling.20underlying.20LLVM.20bugs.20rust.2374498.html#205662138">(Aug 01 2020 at 03:42)</a>:</h4>
<p>(or, on the other hand, it could be a case of all the FIXME's littered in the code that mention <code>AR-&gt;getNoWrapFlags</code> ...)</p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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